Continuous hemispherical contour limit switch for antenna



n- 6 F. w. HAROAWAY CONTINUOUS HEMISPHERICAL CONTOUR LIMIT SWITCH FOR ANTENNA Sheet Filed May 26, 1966 FIG COMMAND IIYII COMMAND llxll X CONTROL 2 R R m m T T A A BR IR E SE N XE G n 8 4 E w g N, 6 2

Y CONTROL INVENTOR.

FRED w HARDAWAY Jan. 7, 1969 F. w. HARDAWYAY CONTINUOUS HEM ISPHERICAL, CONTOUR LIMIT SWITCH FOR.ANTENNA Filed May 26, 1 966 I Sheet aw-m mmwflom llllu Z0583! Q o on N gt 223 7 mm H wk Io. m $4 m am 5:96 FIIIW II IIIL Q R A A M28 :35 52 552 wmwm 932x51 Q mw kn um mm 5x5 mm m% 1052 552053 #555081 mm? ww G mv \n\ \w 5x5 wm :30: i 5520105 P w 53.0mm. Lo mm? mw mm mm 3 8v 9v INVENIOR.

FRED W. HARDAWA Y ATTORNEY United States Patent O 6 Claims ABSTRACT OF THE DISCLOSURE A model antenna is slaved to a primary antenna. A light source and light detector are mounted on the model antenna. When the light beams pass through the light transmissive area of the antenna dome, the interlock circuit is broken and the primary antenna is disconnected from the transmitter.

This invention relates in general to a safety device and in particular to a horizon contour limit switch capable of disabling a high power transmitter when it is pointed in directions likely to injure personnel.

Larger and larger transmitters are being used in radio communication and the transmitted powers have reached levels dangerous to personnel. Certain applications of radio propagation use movable antennas which may be pointed in many directions and when the power emitted from such antennas exceeds certain limits, danger to personnel exists. For example, a transmitted power of 20 kilowatts from a 30-foot antenna system results in a serious R-F radiation hazard to personnel in the immediate area when the antenna pointing angle approaches the horizon. For example, the most common effect of microwave energy on living tissue is heating. The percentage of power absorbed by the human body is normally highest for frequencies between 1 to 3 gigacycles. The effects of successive burns are not cumulative as long as healing takes place between exposures. However, the viscous fluid in the eyes is an exception. This fluid tends to coagulate and at each successive exposure more coagulation occurs without recovery between the exposures. Thus, continuous exposures to high levels of energies at these frequencies can lead to serious damage to the eyes. It has been determined that the power density of 10 mw./cm. is accepted as a maximum safe level for occasional exposure and it has been recommended that l mw./cm. should not be exceeded for prolonged exposure.

A radiation intensity of 10 mw./cm. could normally occur from a 30-foot diameter paraboloid antenna radiating kw. at 2100 me. up to distances of 2300 feet. Thus, when the beam of a 30-foot antenna approaches the horizon, personnel may be subject to excessive radiation if within a 2300-foot radius of the antenna.

It is an object of the present invention to provide a limit switch which will automatically cut oil a high power transmitter if the pointing angle of the antenna approaches the horizon so as to endanger personnel.

Another feature of this invention is to provide a safety device for the protection of personnel.

A feature of this invention is found in the provision for a model antenna which is slaved to a large radiating antenna and which is covered by a dome that has regions which selectively reflect or transmit light. A light source and a light detector are mounted on the model antenna and an interlock circuit is connected to the light detector such that the power to the main antenna is turned off ice when the main antenna approaches pointing angles that are hazardous to personnel.

Further objects, features, and advantages of this invention will become obvious from the following description and claims when read in view of the accompanying drawings, in which:

FIGURE 1 is a view of the model of this invention connected in circuit with the large radiating antenna; and,

FIGURE 2 is a block diagram illustrating the operation of the safety interlock structure.

FIGURE 1 illustrates a large transmitting antenna designated generally as 10 which consists of a parabolic dish 11 which is mounted about a first axis 12 which passes through the rear portion 13 of the dish and a yoe 14. The yoke 14 is pivotally supported on an axis 16 which is supported by suitable stand 17. The antenna 11 and yoke 14 may be driven by suitable motor means which engage drive racks 18 on antenna 11 and rack 19 on yoke 14. The antenna 10 is a conventional antenna and is controlled by command signals fed from leads 21 and 22. An X command signal is supplied to lead 21 and is connected to the X drive mechanism which moves yoke 14 about the axis 16. A Y command signal exists on lead 22 and is connected to the Y drive motor which moves the antenna 11 about the axis 12. The X command signal is produced by an X signal generator 23 which has an input shaft 24 controllable by knob 26. Knob 26 may be moved manually or otherwise and the generator 23 will produce an X command at lead 21 to slave the antenna to the commanded X position. Likewise, a knob 27 commands a selected Y position. A shaft 28 is connected to a Y generator 29 which produces output at lead 22 which drives the Y motor of the antenna 11. Knob 27 is mounted on shaft 28. The X and Y command signals on leads 21 and 22 are also supplied to a model antenna designated generally as 31. The model antenna 31 is mounted on a base 32 and is covered by a translucent dome 33. The translucent dome 33 has a first portion 34 which is painted with a reflective paint and has a second portion 36 which is unpainted. The junction line between the portions 34 and 36, designated as 37, determines the contour of the Zones between which the large antenna 11 is allowed to transmit and is cut ofl. Mounted on the base 32 are a pair of uprights 38 and 39 which carry a generally U-shaped yoke 41 which is supported on a shaft passing through the axis 42. A servomotor 43, tachometer 44 and resolver 40 are mounted on the uprights 38 and 39. The servomotor 43 drives the yoke 41 about the X axis 42. The yoke 41 has a pair of uprights 46 and 47 through which a Y axis 48 extends. A Y servomotor 49 is mounted to upright 46 to drive a detector unit 52 mounted on axis 48. A tachometer 51 and resolver 50 are also mounted to detector unit 52 and to yoke 41. The detector unit 52 has a pair of arms 53 and 54 which carry a light source 56 and a light detector 57.

As shown in FIGURE 2, the X command signal from lead 21 is connected to resolver 40 and the Y command signal from lead 22 is connected to the Y resolver 50.

An X servoamplifier 58 supplies an input to the X motor 43. Mixer 59 supplies an input to servoamplifier 58. The mixer 59 receives a position feedback input from resolver 40 and a rate feedback signal from X tachometer 44.

A servoamplifier 61 supplies an input to the Y axis motor 49 and receives an input from a Y mixer 62. The Y mixer 62 receives an input from the resolver 50 and a rate feedback signal from the tachometer 51.

The light source 56 is driven about the X and Y axis and an output light is reflected from the Plexiglas dome 33 if the light source is pointing toward the reflecting portion 34 of the dome. This reflected light is detected by the light sensor 56. The output of light sensor 56 is sup plied to an amplifier 63 which controls a relay 64. The relay 64 controls a coaxial switch 66 in the power amplifier 67 of the transmitter. The coaxial switch 66 has a movable contact 68 which in a first position engages a contact 69 that connects the transmitter klystron 79 to an exciter 73 and in :a second position engages a contact 71 which is connected to a dummy load 72. The contact 69 is connected to the power klystron so that when contact 68 engages contact 69, the klystron will be energized by the output of the exciter and high powered energy will be radiated by the antenna 11. When the contact 68 is in engagement with contact 71, the klystron will not be energized and the antenna 11 will not radiate.

The Plexiglas dome may be painted in the region 34 with white paint which will receive the light from the light source 56 and reflect it back to the light sensor 57. When the movement of the antenna causes the path of the light source to cross into an unsafe area, the reflected light is reduced because portion 36 of the dome is unpainted and the amount of reflected light received by the light sensor 57 will be substantially reduced. When this occurs, the relay 64 is de-energized and moves the contact 68 to engage the contact 71, thus turning oli the power to the antenna. As long as the light source and sensor are pointed toward a painted area 34 of the dome 33, contact 68 will be in engagement with terminal 69 and the antenna will be radiating power.

It is to be realized that the contour 37 on the Plexiglas dome 33 may be determined by the actual physical surroundings of the large antenna 11 so as to allow the radiation to conform to the actual terrain. For example, valleys and peaks may be followed by the contour 37 to allow radiation as long as hazard to personnel does not occur.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and scope of the invention as defined by the appended claims.

I claim:

1. Means for preventing hazard to personnel from a high powered transmitter with a movable main antenna, comprising a model antenna movable about the same axes as the main antenna and slave to it by a servosystem so as to move with the main antenna at all times, a transparent cover over the model antenna, opaque material placed on said transparent cover to define a first zone which is reflective to energy and a second zone which is transparent to energy, an energy radiator and detector mounted on the model antenna so as to continuously point in the same direction as the main antenna, and an interlock means connected to the detector and to the high powered transmitter to disable it when the main antenna points in a direction hazardous to personnel.

2. Apparatus for preventing hazards to personnel adjacent the main antenna of a high powered transmitter, said main antenna mounted on a pair of axes so that it may be pointed in any direction, comprising a small model of the main antenna mounted on a pair of axes parallel to the axes of the main antenna, a first resolver and first servomotor mounted on the first axis of the model antenna, a second resolver and second servomotor mounted on the second axis of the model antenna, command signals which are supplied to the main antenna supplied to the first and second resolvers of the model antenna, the output of the first resolver supplied to the first servomotor, the output of the second resolver supplied to the second servomotor, a radiating source and sensor mounted on the model antenna and continuously controlled to point in the same direction as the main antenna, a transparent cover mounted over the model antenna and having a first area covered by reflective material such that energy radiated from the radiating source will be reflected to the sensor and having a second area which is not covered by reflective material so that energy will pass through the cover and not return to the sensor, and an output from the sensor connected to the main transmitter to disable it when the main antenna is pointing in a direction which presents a hazard to personnel.

3. In apparatus according toclaim 2, a first tachometer mounted on the first axis of the model antenna and supplying an input to the first servomotor, and a second tachometer mounted on the second axis of the model antenna and supplying an input in the second servomotor.

4. In apparatus according to claim 2, wherein said output from the sensor is connected to a relay which controls a switch in the main transmitter to disconnect the main power from the main antenna.

5. In apparatus according to claim 2, wherein the main antenna and the model antenna are mounted on X-Y axes.

6. In apparatus according to claim 2, wherein the radiating source emits visible light and the sensor detects visible light.

No references cited.

ROBERT L. GRIFFIN, Primary Examiner.

A. I. MAYER, Assistant Examiner.

US. Cl. X.R. 

